Measurements

The Mark 8 weighed 121,856 pounds (55,273 kg) including the breech and was capable of an average rate of fire of 2.4–3 rounds a minute. It could throw a 1,140 lb. (517.093 kg) Mark 18 armor piercing shell 38,573 yards (35,271 meters) at an elevation of 45°, while the "barrel life" of the guns was 344 shots;
when compared to the 16"/50 caliber Mark 7 gun found in the Iowa-classbattleships, Alaska-cruisers could fire about 54 more shots.[1][3]

As a result of the decision to fire "super heavy" armor piercing projectiles, the Mark 8's deck plate penetration was better and the side belt armor penetration equal to the older (but bigger) 14"/50 caliber gun.

The previous 12" gun manufactured for the U.S. Navy was the Mark 7 version, which had been designed and installed in the 1912 era Wyoming-class battleships.[1] The Mark 8 was of considerably higher quality; in fact, it "was by far the most powerful weapon of its caliber ever placed in service."[4]